1) Technical Field of the Invention
The present invention relates to a process of forming an embedded copper wire, and in particular, relates to process of forming the embedded wire by electroless plating.
2) Description of Related Arts
A damascene process can be utilized to obtain a high density of semiconductor devices. In the damascene process, flat circuits are formed with patterned wires of copper that are embedded In an insulating layer. In the damascene process, first, a hole and/or trench is formed on the insulating layer. Then, a barrier metal layer of metal such as TaN and WN is deposited on the inner side wall of the hole by sputtering or chemical vapor deposition (CVD). Since the barrier metal has a high electric resistance, a seed layer of copper having thickness of around 10 mn is laminated on the barrier metal layer by sputtering. Lastly, an electroplating process is used to form a copper layer on the seed layer and fill up the hole so that the embedded wires of copper are completed.
The high density and the fine pitch of the patterned wires of the semiconductor device hamper formation of the homogeneous seed layer in a sputtering operation. For example, as the aspect ratio of the hole and/or trench is increased, it is more difficult by a sputtering operation to achieve formation of the homogeneous seed layer on the inner side wall thereof. The side coverage on the walls is substantially reduced. Thus, the electroplating process for forming the plating layer on the seed layer is inadequate to fill up the fine bole with homogenous copper plating layer.
A particular and expensive sputtering systems such as the advanced ionized directional sputter deposition system and the long distance sputter deposition system may be used to improve the side coverage of the seed layer. Nonetheless, such systems may make the conventional electroplating process available for at most another generation in the innovation of the semiconductor devices, and eventually, the conventional electroplating process for forming the embedded wire would dead-end.
Therefore, the present invention provides a process for forming the embedded wires with higher density and with finer pitch, but without using a catalyzing agent.